The present invetion relates to a roof assembly for an electric arc furnace used for melting metals and has particular application in a roof assembly of the type where a number of water cooled roof segments or panel units are arranged to have their sides abutting each other and an outer support ring encircles the periphery of the roof.
Past designs for a roof of an electric arc furnace include several different types, the most common being of the spherical dome configuration formed either by refractory bricks or by water cooled panels, such as those roof designs disclosed in U.S. Pat. Nos. 4,021,603 and 4,216,348. Other roof assemblies have roof composites such as refractory bricks or tiles to form a flat disposed roof over the furnace, such as those disclosed in U.S. Pat. Nos. 4,063,028 and 4,132,852.
The central area in most of these past designs is commonly referred to as a "delta area" where the openings or ports for the electrodes are located, and which may consist of an assembly of bricks which may or may not be surrounded by a water cooled inner ring. This electrode area usually is a high wear area. The refractory bricks depend on each other for their support in the spherical dome shaped roof designs and deterioration of any of these refractory bricks could cause collapse of the delta area or would cause failure or collapse of the entire roof especially in the instance where the refractory bricks comprise the entire roof assembly.
In the roof designs which are in a flat disposition, such as that of the above '852 patent, it is still mandatory to replace the refractory bricks frequently after a certain number of heats of the furnace.
In most of the above described water cooled roof designs, refractory bricks are still being used in the delta area since any metal components in this area would have the tendency to overheat as a result of induced electrical currents, thereby resulting in extreme heat build-ups in the metal components; and also the existence of any metal components in this vital area near the electrodes would have the tendency to create arcing between the electrodes and the metal components.
In these dome-shaped configurations for the above described roof designs, the water cooled panels or refractory bricks abut the outer cooled ring means which is supported by the sidewalls of the furnace shell. The proximity of these panels or bricks along the boundary line of the top of the furnace shell with the roof assembly makes these panels or bricks of the roof assembly suspectible to several disadvantages, thereby decreasing the operation of the furnace. These disadvantages are: (1) arc flair reflected from the furnace sidewalls; (2) elevated radiated heat fluxes; (3) mechanical failure and abuse to the components of the roof from charged scrap in the furnace, and (4) electrical arcing from the scrap to the roof assembly due to the closeness of the roof to the scrap.